The present invention relates to an inspection system and the like for an active matrix panel in used such as an organic EL and an inorganic EL, and more particularly to an inspection system and the like for performing inspection by causing a probe to contact pixel electrodes.
Recently, of various display panels, an EL panel incorporating therein an organic EL (Electro Luminescence) or an inorganic EL has been increasingly attracting attention. An EL device is a chemical material, self-emitting when electrified, and is capable of emitting lights of different colors by altering a chemical structure thereof. The EL device has been studied for various applications. Among other devices, the EL device (hereinafter, referred to as an OLED (Organic Light Emitting Diode)) is caused to emit light when fluorescent organic compound excited by applying an electric field thereto is charged with direct current. The EL device has been attracting attention as a next generation display device in terms of achievement of thin depth, wide viewing angle, wide Gamut and the like. Methods for driving the OLED include a passive matrix type and an active matrix type. To pursue a larger screen and a higher resolution display, the active drive type is preferable in terms of materials, life time, cross-talk. For the active drive type, generally, a TFT (Thin Film Transistor) drive method has been employed.
Then, an active matrix OLED (AMOLED) and an active matrix liquid crystal display (AMLCD) be explained while comparing those two devices with each other. FIGS. 21(a) and 21(b) are diagrams to explain and compare pixel circuits for an AMOLED and an AMLCD. FIG. 21(a) illustrates a pixel circuit for an AMOLED, and FIG. 21(b) illustrates a pixel circuit for an AMLCD. Referring to FIG. 21(b), a TFT 310 connected to a data line and a gate line constitutes a pixel circuit for a TFT array. In the AMOLED shown in FIG. 21(a), a driver TFT 302 as a drive transistor having an open drain configuration is, disposed adjacent to, and connected to, a pixel capacitor of a circuit similar to that shown in FIG. 21(b), and an OLED 301 as a light emitting device is connected to the driver TFT 302. The AMLCD of FIG. 21(b) is capable of altering gradation merely by generating a voltage in the TFT 310 therein. The AMOLED, when a prescribed voltage is applied to the driver TFT 302 therein, alters brightness of the OLED 301 depending on the quantity of current flowing through the OLED. It is likely that a threshold voltage Vth of the driver TFT 302 varies even if the process is adjusted. In case of occurrence of the variations, even when the same voltage is applied to the TFT, currents flowing through the TFT is different from one another in quantity, causing variations in the brightness. For this reason, when functions of TFT arrays for an AMOLED panel are inspected, in addition to checking whether interconnects are open or short circuited, it is important to check whether characteristics of the driver TFTs 302 for driving the OLEDs 301 are uniform throughout the entire panel. This inspection is to confirm that a compensation circuit for the driver TFTs 302 functions normally, and that the Vths of the driver TFTs 302 on the panel are uniform.
To reduce manufacturing cost of a conventional AMOLED panel, TFT arrays are required to be inspected as a single unit so that only a non-defective unit is sent forwards to the subsequent step, such as a step of forming an OLED. In the manufacture of AMOLED panel, currently, yield of TFT arrays for a conventional AMOLED is not sufficiently high, and materials for the OLEDs 301 themselves are expensive. In addition, it takes longer time for the OLED 301, among other things, to be manufactured. For those reasons and others, before manufacturing the OLEDs 301, it is desirable to measure the Vths of the driver TFTs 302. However, with regard to the TFT array as a single unit, OLEDs as components of pixel circuits are not yet mounted thereon, and the driver TFT has an open drain configuration. That is, in steps before the mounting of OLEDs, the OLED 301 as denoted by a broken line of FIG. 21(a) is not connected and does not constitute a normal circuit. Accordingly, it is basically impossible to pass current through the driver TFT 302, and inspection and the like of functions of a Vth compensation circuit normally functions cannot be performed as long as the OLED 301 is not connected. To inspect such a driver TFT 302, an approach to applying a voltage to an electrode in an open state from outside or an approach to pulling down a potential of the electrode to a GND (ground) is needed.
For example, as a conventional technology described in the patent publication, an inspection method has been proposed in which TFT arrays are immersed in electrolytic solution, and are made electrically conductive, and then, a voltage is applied to the arrays (e.g., refer to a patent-related reference 1). Furthermore, another inspection method has been described in which, for example, before formation of a pattern of pixel electrodes, a conductive film for inspection is formed on an upper portion of the pixel electrodes to perform inspection and the film is removed after the inspection (e.g., refer to a patent-related reference 2). Moreover, although a technology has nothing to do with solution to technical problems, the technology has been proposed in which a cylinder-shaped rotatable probe is caused to contact interconnect extensions while being rotated, and accordingly electrical characteristics of electrodes are inspected (e. g., refer to a patent-related reference 3).    [patent-related reference 1] Japanese Unexamined Patent Publication 2002-72918 (pp. 4–5, FIG. 1)    [patent-related reference 2] Japanese Unexamined Patent Publication 2002-108243 (pp. 8–9, FIG. 1)    [patent-related reference 3] Japanese Patent Laid-Opened Official Gazette No. SHO-63-5377 (pp. 2–3, FIG. 1)
However, according to the technique disclosed in the patent-related reference 2, the conductive film for inspection is formed layered on the upper portion of TFT arrays and closely contacts the pixel electrodes. Accordingly, in practice, the step of forming the conductive film on the upper portion of the TFT arrays and the step of removing the film have large adverse effect on the TFT arrays, and it is highly likely that damage is caused to surfaces of pixel electrode circuits with high probability. Furthermore, according to the technique disclosed in the patent-related reference 1, the TFT arrays need to be immersed in electrolytic solution and therefore it can be concluded that the technique is not practical.
Additionally, when semiconductor components are inspected, a probe system (prober) is employed as a system for making electrical contact. This probe system, made of needles such as thin metal needles and conductive rubber needles, causes the needles to contact electrode pads for inspection. As a probe head used in a conventional probe system, for example, a contact probe formed by integrally molding resin of anisotropically conductive material has been proposed. An example is a probe designed to allow electrical conduction only between upper and lower projections for contact. Moreover, when semiconductor components are inspected, contacts to tens to hundreds of electrodes make the inspection sufficient. Thus, elasticity of spring and rubber, tension of metal needles as well as pressurization by using pressure of the surrounding atmosphere enable the contacts to be made securely. However, in the case of an AMOLED panel, contacts should be made to more than hundred thousands of electrodes arranged in a matrix, and therefore it is difficult to apply equal pressure to all the probes. By contrast, a system is also conceived which causes individual inspection needles to be independently controlled to apply pressure to individual pixels. However, a system for making contacts to more than hundred thousands of electrodes is very difficult to assemble, and becomes expensive. The patent-related reference 3 only discloses a technique for pressing a probe against interconnect extensions, and never discloses a technique for making direct contact to electrodes arranged in a matrix. Therefore, the technique disclosed in the reference 3 never addresses the problems arising when TFT arrays for OLEDs are inspected before formation of the OLED and cannot be utilized to solve the problems.